Node.js查询性能测试异常：后执行查询始终更快的问题排查

DevOps 小满

2026-7-9

PostgreSQL查询性能测试异常：第二个查询总是比第一个更快

我编写了一个简单的Node.js程序用于测试PostgreSQL查询性能，但遇到异常：当循环执行查询数组时，第二个查询总是比第一个更快。例如数组为[A,B]时B更快，改为[B,A]时A更快，但单独执行任一查询或在psql中执行时，两者性能几乎一致。

相关代码

index.js

const { Client } = require('pg');
const queryPref = require('./src/QueryPref');

require('dotenv').config();

(async ()=> await queryPref())();

queryPref.js

const { Client } = require('pg');


const queries = [
  {
    'queryStr': 'SELECT * FROM tabluno where user_name = $1',
    'options': ['08544f75d007ae439925bb21fe48c64c'],
  },
  {
    'queryStr': 'SELECT * FROM tabluno2 where user_name = $1',
    'options': ['f67a10e60fde706bb6c5948374b385e5'],
  },
]

function initClient() {
  console.log('opening a new connection');
  const client = new Client({
    user: 'postgres',
    host: 'localhost',
    database: 'indexing-is-really-hard',
    password: process.env.DB_PASSWORD,
    port: 5432 // default port for postgres
  });

  return client;
}

async function queryPref() {
  for(const query of queries) {
    let pool = new Client({
      user: 'postgres',
      host: 'localhost',
      database: 'indexing-is-really-hard',
      password: process.env.DB_PASSWORD,
      port: 5432, // default port for postgres
    });

    await pool.connect();
    await pool.query('SELECT 1');

    let avg = 0;
    for(let i = 0; i < 1000; i++)    {
      const start = performance.now();
      await pool.query(query.queryStr, query.options)
      const end = performance.now();
      avg += end - start;
    }
    avg /= 1000;

    console.log(`${query.queryStr} took an avg of ${avg.toFixed(3)}ms`)

    pool.end();
    pool = null;
  }
}


module.exports = queryPref;